A memory component comprises a memory integrated circuit (IC) mounted on a chip carrier. The memory component may include a resin package with external leads for mounting the component to an external surface of a multilayer printed circuit board. Other electronic components such as capacitors can also be mounted on the external mounting surfaces. Multilayer printed circuit boards used for these purposes typically include insulating layers, wiring layers between the insulating layers, and wiring layers on the external surface of the multilayer printed circuit board. The external leads of each memory component are typically soldered to pads or other conductors printed on the external surface of the multilayer printed circuit board.
FIG. 1 illustrates a memory module 1 according to the prior art. Memory components 3A, 3B, 3C each comprise an IC mounted on a chip carrier surface and molded in resin material (not shown). The memory components are mounted on an external mounting surface of a multilayer printed circuit board 4. Each memory component has external metal leads 5 soldered to metal pads (not shown) on the external mounting surface 7. A capacitor 2 is also mounted on the external mounting surface. A row of electrical contacts 6 is also shown on the edge of the multilayer printed circuit board to provide electrical contact to other printed circuit boards. U.S. Pat. No. 5,412,538, to Kikinis et al, entitled Space Saving Memory Module, issued on May 2, 1995 depicts a similar memory module as that shown in FIG. 1.
In the memory module 1 described above, heat generation by the ICs increases as the operating speed of the ICs is increased. Total heat generation is also increased by an increased number of ICs, often stacked (in stacked memory modules), needed to increase memory density and performance. Each IC dissipates heat directly into the surrounding air and from the external leads 5 and the metal pads on the external mounting surface to the surrounding air.
The path from the metal pads to the surrounding air is not very effective because there is usually resist or solder mask covering the pads. Furthermore, the external surface of the multilayer printed circuit board is typically comprised of a resin material which has a low heat transfer coefficient. While the direct heat dissipation from the memory component to the surrounding air is more effective than through the printed circuit board, the total heat dissipation is often insufficient to maintain the ICs at the desired temperature especially where the memory components are stacked. Therefore optimal performance cannot be obtained.
Multilayer rigid/flexible printed circuit boards are also known in the field. Typically, a rigid/flexible printed circuit board includes a flexible printed circuit board portion which extends from the periphery of a rigid section or sections with the rigid sections being used for mounting mechanical hardware of electrical components. Circuit boards having these flexible portions offer numerous advantages over standard rigid printed circuit boards. They are easier to handle and can be used where limited space is required since they can be inserted in virtually any shape or space in a system and occupy less space in that system. Also, they offer the advantage of allowing the rigid section of the printed circuit board to be mounted or located in one area, where space is at a premium, allowing the flexible portion to be mounted in a remote area away from the area in which the rigid section is located.